The present invention relates to fuel injectors of fuel cells, and more particularly to a diagnostic system for identifying fuel injector failure in a fuel cell system.
Pulsed fuel injectors are used to control the delivery of fuel in internal combustion engines of vehicles. Pulsed fuel injectors are also typically used with fuel cell systems that convert liquid fuel to a hydrogen-rich gas stream. Pulsed fuel injectors are proven, robust, and cost effective due to experience gained from their use in internal combustion engines.
Conventional methods for diagnosing degradation and failure of a fuel injector in internal combustion engines are inadequate for fuel cell applications. Diagnostic systems for internal combustion engines typically check for negative effects of a failed fuel injector. For example, a vehicle On Board Diagnostic (OBD) method monitors cylinder misfires. When an injector fails, the failed injector causes a momentary decrease in crankshaft speed. A position sensor detects the decrease and triggers a check engine light.
In internal combustion engines, an injector typically fails in a closed position, which does not harm the engine. A short term misbalance between fuel, air and spark does not typically impact engine durability. In a fuel cell fuel processor, however, the balance of inputs is more critical. A proper balance between fuel, air, and water keeps the fuel processor catalysts in proper working condition.
If the fuel injector fails while running, the fuel processor temperature begins changing. If the injector fails in the near closed position, temperature may rise due to a higher oxygen to carbon ratio (O/C). If the injector fails fully closed or open, temperature will eventually drop. Since the fuel processor has appreciable mass, the temperature drop may not occur quickly. During this time, water and air are reaching the fuel processor components without proper reactions taking place, which may harm the fuel processor components. Also, any change in temperature may be caused by other problems such as incorrect air or water. Therefore, monitoring temperature does not necessarily identify a failed injector.
If the fuel injector fails during startup, the system may run for several minutes before detection. Temperatures often takes a significant amount of time to rise in a cold fuel processor, even with a working fuel injector. A failed injector cannot be diagnosed based on temperature until long after the first fuel command. By this time, a significant amount of incorrect fuel has been supplied to the fuel processor.
Fuel flow sensors can be used to diagnose a failed injector. Fuel flow sensors are expensive and typically have moving parts that may fail. Fuel flow sensors add cost, size, and weight, reduce reliability and have wiring and controller I/O requirements.
A diagnostic system and method identifies fuel injector failure in a fuel cell system including a fuel processor and a fuel source. A fuel injector supplies fuel from the fuel source to the fuel processor. A pressure sensor generates a pressure signal based on pressure between the fuel source and the fuel injector. A fuel injector diagnostic identifies fuel injector failure based on the pressure signal.
In other features, a fuel pump pumps fuel from the fuel source to the fuel injector. A regulator communicates with the fuel tank and regulates pressure between the fuel pump and the fuel injector. The fuel injector diagnostic is implemented using a controller with a processor and memory.
In still other features, the fuel injector diagnostic includes a moving window tracker that tracks the pressure signal over a moving window. The fuel injector diagnostic further includes a standard deviation calculator that generates a standard deviation based on the pressure signal in the moving window. Alternately, the fuel injector diagnostic includes a variance calculator that generates a variance based on the pressure signal in the moving window.
In still other features, the fuel injector diagnostic includes a diagnostic enabler that enables the fuel injector diagnostic. The diagnostic enabler includes a comparator that receives an injector command and an injector command minimum signal. A noise reducer communicates with the comparator and transitions from low to high after a first period after the comparator signal goes high and from high to low after a second period after the comparator signal goes low.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.